This research program focuses on the development of new synthetic strategies for the total synthesis of biologically active complex alkaloid natural products. Within each total synthesis goal lies the implicit aim of discovering and exploiting new reactions that push the boundaries of chemical synthesis innovation. In this context, new strategies for the total synthesis of several guanidine-containing complex alkaloids will be explored. These classes of targets include the family of anti-HIV/immunomodulating batzelladine alkaloids, the family of anticancer and ion-channel disrupting crambescidin alkaloids, the potent cytotoxin cylindrospermopsin, and the powerful immunosuppressant palau'amine. All of these natural products exhibit significant yet distinct biological responses, yet they are all structurally characterized by at least one guanidine moiety embedded within a complex polycyclic architecture, a synthetic challenge that will be addressed by investigating novel annulation strategies and reactions for nitrogen-heterocycle synthesis. These proposed goals will involve investigation of diastereoselective [4+2]-annulation of vinyl carbodiimides with chiral imine and imidate derivatives for dihydropyrimidine and pyrimidine synthesis, as well as other convergent cycloaddition strategies for the construction of fully substituted all-cis cyclopentanes. Successful synthesis of these target molecules will not only lay the foundation of efficient and practical strategies for complex alkaloid synthesis, but also provide access to complex natural products of biological interest and therapeutic potential in a variety of health areas, including small molecule cytotoxic/anticancer, antiviral, and immunomodulating agents, as well as unique heterocyclic constructs that specifically disrupt ion channel function. [unreadable] [unreadable] [unreadable]